(a) Technical Field
The present invention relates to a driving control method and system of a fuel cell system, and more particularly to a driving control method and system of a fuel cell system that improve the drivability of a vehicle and durability of a fuel cell.
(b) Background Art
Fuel cell vehicles include a fuel cell stack composed of a plurality of fuel cells stacked and used as a power source, a fuel supply system that supplies hydrogen (e.g., fuel) to the fuel cell stack, an air supply system that supplies oxygen that is an oxidizer for an electrochemical reaction, and a water/heat management system that adjusts the temperature of the fuel cell stack. The fuel supply system depressurizes compressed hydrogen in a hydrogen tank and supplies the compressed hydrogen to the anode of the stack and the air supply system supplies suctioned external air by operating an air blower to the cathode of the stack.
When hydrogen is supplied to the anode of the stack and oxygen is supplied to the anode, hydrogen ions are separated by a catalytic reaction from the anode. The separated hydrogen ions are transmitted to the oxidizing electrode, which is the cathode, through an electrolyte film and the hydrogen ions separated from the anode create an electrochemical reaction with electrons and oxygen at the oxidizing electrode to obtain electric energy. In particular, electrochemical oxidation of hydrogen occurs at the anode, electrochemical reduction of oxygen occurs at the cathode, electricity and heat are generated by movement of electrons generated in the reactions, and vapor or water is produced by a chemical reaction created by bonding of hydrogen and oxygen. In addition, a discharge unit is provided for discharging hydrogen and oxygen that do not react with the byproducts such as the vapor, water, and heat generated in the process of generating electric energy of the fuel cell stack, and the gases such as the vapor, hydrogen and oxygen are discharged to the atmosphere through a discharge channel.
In addition, fuel cell hybrid vehicles have been developed to make up for defects that may be generated when using only a fuel cell as a power source of vehicles. The fuel cell hybrid vehicles include a high-voltage battery or a super capacitor other than a fuel cell that is the main power source. The fuel cell hybrid vehicles use a fuel cell, as the main power source, which is supplied with hydrogen from a hydrogen tank and air from an air blower and generates electricity, using an electrochemical reaction of the oxygen of hydrogen and air. A driving motor and a motor controller are connected directly to the fuel cell via a main bus terminal and a super capacitor is connected via an initial charging unit for power assist and regenerative braking. Further, an LDC (Low Voltage DC/DC Converter) for converting output between a high voltage and a lower voltage and a low-voltage battery for driving parts are connected to the main bus terminal.
The components such as an air blower, a hydrogen recirculation blower, and a water pump, which activate the fuel cell, are connected to the main bus terminal and facilitate starting of the fuel cell, and various relays to facilitate connection and disconnection of power and a diode that prevents backward current to the fuel cell may also be connected to the main bus terminal.
Further, dry air supplied through the air blower is humidified through a humidifier and is then supplied to the cathode of the fuel cell stack and the gas discharged from the cathode is humidified by the water produced inside and is transmitted to the humidifier, and may be used to humidify the dry air to be supplied to the cathode by the air blower. The phenomenon that the hydrogen remaining at the anode directly passes an electrolyte film without generation of electricity and reacts with the oxygen at the cathode is called “hydrogen crossover” and is required to decrease the anode pressure at the low-output period and increase the anode pressure at the high-output period to reduce the amount of hydrogen crossover. The greater the anode pressure (e.g., hydrogen pressure), the greater the increase of the amount of hydrogen crossover and the hydrogen crossover may have a negative influence on the fuel efficiency and the durability of the fuel cell, and thus maintenance of appropriate anode pressure is required. A hydrogen purge valve is provided to ensure stack performance by discharging impurities and condensed water at the anode side and an anode exit terminal is connected with a water trap to store the condensed water and then discharge the condensed water through the valve when the amount of the condensed water reaches a predetermined level.
To improve the fuel efficiency as mentioned above, the process of stopping and restarting the fuel cell generating electricity while the vehicle travels (e.g., Fuel Cell Stop/Fuel Cell Restart), if necessary, that is, the idle stop/go control process of temporarily stopping the fuel cell generating electricity in fuel cell hybrid vehicles (e.g., On/Off of fuel cell) should be considered as being important. In particular, when stopping and restarting the fuel cell generating electricity while a vehicle travels, the control, which generally considers not only the problem of dry-out in the fuel cell stack, but also reacceleration performance and fuel efficiency of the vehicle is important.
The description provided above as a related art of the present invention is merely for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.